The invention concerns an expansion tool for hollow, in particular hollow cylindrical working parts with a basic tool body and a borehole, and an expanding mandrel located in this borehole in an axially slidable position and having an exterior tapered end protruding from the borehole. A swivelling control device also located in the basic tool body which acts on the expanding mandrel through a free rotating cylinder has an axis perpenicular to the borehole axis, and is connected to a hand lever which, when activated, causes the expanding mandrel to emerge from the basic body (2), sliding at a preset stroke against a set (15) of radially moving expanding wedges.
These types of expanding tools are also called "Expanders". They are used like tongs, i.e. the swivel hand lever has a second hand lever of the same length, which is rigidly connected to the basic body. Expanders are mainly used to expand the ends of pipes to the extent necessary to allow the introduction of a second, non expanded pipe end into the expanded area, and to weld it to the first pipe end. It is used in construction sites and in workshops.
The operating forces are determined by the transmission ratio in the operating system of the expanding mandrel, by the friction ratio between all the movable parts and--not least--by the flow of the material of the working part to be expanded. The following materials are suitable: plastic pipes, thin walled soft steel pipes, but mainly copper pipes, annealed as well as so called "hard" copper pipes. These tools are preponderantly used in the construction of pipes, particularly in the sanitary and installation fields.
In view of the ergonomic relations, it should be noted that the angle of traverse of both hand levers in relation to each other, taking into account the transmission ratio, is slightly over 90 degrees. Since in this situation the actual power stroke occurs relatively early, the two hand levers are at a relatively unfavourable position to each other at the start of the power stroke. Since normally the basic tool body cannot be supported anywhere, the effective operating forces can only run parallel to the axis of the expanding mandrel; all other reaction forces must be additionally absorbed by the person operating the device. For instance, it is not possible at the beginning of the power stroke to load the hand levers running radially in relation to the swivel axis of one of the hand levers, in a purely tangential direction (then the operator would pull the basic tool body towards himself), instead purely paraxial forces must be applied. Mechanically this is expressed in such form, that the effective length of the hand levers, which at this point form a 90 degree angle, is drastically shortened. The ratios do improve as the hand levers approach each other, which to a certain extent compensates for the increasing deformation forces during the expanding procedure, but depending on the chosen type of operation, can also cause the operating forces to drop off drastically towards the end of the power stroke, leaving the operator without any "feel" regarding which forces and reaction forces are released inside the operating system.
In the course of the development of this type of tong like expanders, the following operating systems were created:
In the expander according to GB-PS 866 994 (Rast) an eccentrically positioned cam acts directly on the bevelled back of the expanding mandrel. This causes the development of tangential power components in relation to the cam curve, and radial components in relation to the expanding mandrel, which press the expanding mandrel against its bearing, thus also producing together with the increasing deformation forces of the working part, increased sluggishness. The expanding mandrel becomes in a way the brake shoe for the cam, so that the operating forces progressively increase during the expanding procedure. Another disadvantage of this operating system resides in the fact that the expanding mandrel cannot be retracted. Since the return springs of the expanding wedges act as an automatic lock opposite the expanding mandrel, the expanding wedges with their control surfaces, which can be seen as cone sectors, cannot produce the retraction of the expanding mandrel. In the case of shrinking working parts, as is the case during the expanding of plastic pipes, this kind of expander cannot be easily dislodged from the pipe.
In a further development of this operating principle according to GB-PS 1 485 098 (Rothenberger), the power requirements for the axial sliding of the expanding mandrel were reduced by flattening the course of the curve of the cam, and the full stroke of the expanding mandrel was attained by operating the cam repeatedly and adjusting it after each stroke. For this purpose the cam axis is placed in two cranks with axially staggered recesses. However, the force economy due to the changed transmission ratio and the resulting lengthening of the operating path, was very limited because the braking effect of the expanding mandrel on the cam surface remained practically unchanged. With this known system an enforced withdrawal of the expanding mandrel was absolutely impossible, since traction could neither be applied on the hand lever nor on the cam because of the connecting link guide. A compression spring placed between the expanding mandrel and the basic tool body was only able to produce a certain arresting effect on the connecting link guide, but not the enforced withdrawal of the expanding mandrel. U.S. Pat. No. 4,890,472 discloses an expander which makes possible the enforced withdrawal of the expanding mandrel, and with it a return of the expanding wedges to the starting position, possible thanks to a tension member between the expanding mandrel and the hand lever. However, the high driving forces remained the same as in the expander according to GB-PS 866 994.
In the operating system according to U.S. Pat. No. 4 425 783 the friction forces between the cam and the expanding mandrel on one hand, and the expanding mandrel and its drive (borehole) on the other hand are eliminated to a large extent, although without providing the means for the enforced withdrawal of the expanding mandrel. This is accomplished by placing a swivelling hammer shaped compression member between the expanding mandrel and the cam, since the course of the curve of the cam, and of the surface of the compression member which rolls over it, is such that the axis of the expanding mandrel always intersects the common line of contact of the cam and the compression member. IN order to always start from the same initial position of the compression member, the latter has a return spring. However, when the power stroke is interrupted, the compression member falls back under the effect of the return spring, and the prior existing correlation between cam and compression member no longer exists. However, because of the complicated bearing of the cams and the hand levers, this known system creates friction forces in another place, namely on the perimeter of two relatively large circular disks with which the hand levers and the cams are mounted in the basic tool body. In this case the basic tool body acts, opposite the above mentioned circular disks, as a braking device under the influence of the axial operating forces.
An operating system is known according to U.S. Pat. No. 4,735,078 in which low driving forces are paired with the enforced withdrawal of the expanding mandrel. This is accomplished by placing an elbow lever between the hand lever, which does not have a cam, and the expanding mandrel. This example has a disadvantage compared to the Expander according to U.S. Pat. No. 4,425,783, namely that on one hand the slanted position of the elbow lever at the start of the working stroke creates transverse force components which act on the expanding mandrel, increasing the friction between the expanding mandrel and its bearing (borehole), on the other hand the elbow lever drive has the particularity that the output forces created thereby go towards infinity when the driven parts hit a stroke while all links of the elbow lever system are completely stretched. If tolerances fall below normal values, particularly tolerances in the accessory parts which usually include several sets of expanding wedges of different diameters, an overstrain can occur which the operator would not notice because there is no corresponding increase in the operating force. Experience has shown that with the use of an elbow lever drive in an expander, the force requirements at the end of the working stroke are practically zero, i.e. the hand levers can be put together, almost without requiring any force. Consequently the operator loses any "feel" for the expanding procedure. Usually elbow lever presses are equipped with overload clutches in order to prevent an overload when all three elbow lever links are stretched, and consequently avoid the destruction of the system. The installation of overload clutches is however not possible in the case of hand tools for space and weight reasons.
An expansion tool of the type described at the beginning is known through patent DE-GM 88 07 784 (WO 88/00503), in which the free rotating cylinder consists of a roller whose cylinder surface, the so called rolling surface for the control mechanism, is placed in a complementary recess which runs transversally to the axis of the expanding mandrel. But this reduces the friction between the cam and the expanding mandrel only negligibly, because the roller slides in its recess with the cylinder surface, i.e. with the same diameter on which also the cam surface rolls. This merely causes the shifting of the friction and braking forces to another place, or the cam will slide on the stationary surface of the roller even in case of a slight slow down. Such a mechanical system is also called "indifferent". It does not produce any changes in the friction and in the transversal forces.